Two cards are drawn together at random from a well-shuffled pack of 52 playing cards. What is the probability that both of them are aces?

Two cards can be chosen in $C(52,2)=1326$ ways and two aces in $C(4,2)=6$ ways, so the probability is 6/1326 = 1/221. The same value comes from (4/52) × (3/51). Using 4/52 twice, that is $(1/13{)}^2=1/169$, would be correct only if the first card were put back.